Test of meantimer


Eric Liatard


January 1999

1. Test of meantimer and CFD

1.1 Method

A schematic diagram of the experimental setup is shown in fig. 1.1. The annihilation photons of a 22Na source are detected in coincidence by a thin plastic BC412 scintillator and by a NE110 scintillator (84.5 $\times$ 3.4 $\times$ 1.0 cm3).

Both extremities of the NE110 scintillator are connected to XP2020 photomultipliers (PM1 and PM2). The PMstart can be moved, together with the source, along the NE110 from the middle position (x=0) to x=$\pm$ 35 cm.

Constant Fraction Discriminators (ISN 4351) with 50 mV threshold are used to generate the logic signals entering the meantimer and/or the TDC.

The propagation time along 70 cm of the NE110 scintillator is of the order of 4 ns and the attenuation of the light between the extremities resluts is in the ratio 1/4 : VPM1 $\approx$ VPM2 $\approx$ 400 mV for x=0
VPM1 $\approx$ 800 mV and VPM2 $\approx$ 200 mV for x=35 cm .

With this setup one can test the combined effect of detection position and amplitude variation in the CFD on the timing output of the meantimer

It should be noted that the scintillators, PM and PM bases are different from those which will be used in the G0 experiment.


  
Figure 1: Experimental setup for meantimer and CFD tests.
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1.2 results

The central position of the peak of coincidence between the start signal and the meantimer output is plotted in fig. 1.2 as a function of the x position. The maximum variation of the peak centroid position is 180 ps.


  
Figure 2: Central position of the peak of coincidence between the start signal and the meantimer output as a function of the x position.
\begin{figure}\centerline{\epsfig{width=10cm,file=mean2.eps}} \end{figure}

2. Test of meantimer

2.1 Method

To eliminate the influence of amplitude variations on the CFD and to test the meantimer only, the experimental setup in fig. 2.1 was used. The output of a single PM is distributed in order to obtain a start signal and two delayed signals. The delay difference $\Delta$ t2 - $\Delta$ t1 was varied in the range $\pm$ 10 ns which corresponds to the range of the meantimer compensation.


  
Figure 3: Experimental setup for meantimer tests.
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2.2 results

The central position of the peak of coincidence between the start signal and the meantimer output is plotted in fig. 2.2 as a function of time difference $\Delta t_2 - \Delta t_1$. The maximum variation of the peak centroid position is 120 ps.


  
Figure 4: Central position of the peak of coincidence between the start signal and the meantimer output as a function of the time delay difference.
\begin{figure}\centerline{\epsfig{width=10cm,file=mean4.eps}} \end{figure}